The use of carbon fiber for high temperature composite applications is of growing interest. Greater adaptability, however, is dependent at least in part to achieving improvements in handleability of the carbon fiber yarn in processing and in the production of composites with good resin dominated mechanical properties, such as compressional properties and interlaminar shear strength. The use of agents which might permit attainment of these objectives is limited to those which can withstand high temperatures encountered in production and use of parts from the composites. Thus, standard epoxy sizes are unacceptable since they are unstable at the temperatures required in the cure cycles. Attempts to use these sizes would lead to degradation at the interface between the fiber and resin matrix where good adhesion is vital to obtaining the desired mechanical properties. Unsized carbon fiber has poor handling characteristics leading to severely reduced yields and poor quality when the fiber is woven.